In an operation of an industrial robot, an angle of a joint of a manipulator calculated by a processor, such as a CPU, for activating the joint is correlated to an actual angle of the joint. For this purpose, an origin, being a reference of a rotation of the joint is adjusted.
FIG. 6 shows a conventional apparatus for adjusting the origin disclosed in Japanese Patent Laid-Open Publication No. 2-180580. Member 611 rotates about rotation axis 620 with reference to member 612. Recess 613 is provided in the circumference of member 611 at a position corresponding to an origin. Adjusting device 630 detachable from member 612 is attached to the position corresponding to the origin. Adjusting device 630 includes switch holder 615 fixed on member 612 at the position corresponding to the origin, switch 614 held by switch holder 615, straight bearing 616 mounted on switch holder 615, and sliding rod 617 movable guided by straight bearing 616. Switch 614 includes on/off movement 614A. End 617A of sliding rod 617, a positioning member, is engaged with on/off movement 614A. When sliding rod 617 moves away from switch 614, other end 617B is put into recess 613 provided in member 611.
FIG. 7 shows another conventional apparatus of adjusting an origin disclosed in Japanese Patent Laid-Open Publication No. 2002-239967. Member 712 is coupled rotatably with member 711, so that surface 712A of member 711 contacts surface 711A of member 711. Detachable positioning member 722 is mounted detachably to mounting port 723 of member 711. Member 712 has contact point 721 for contacting positioning member 722. Positioning member 722 is a positioning pin, while mounting port 723 is a tapped hole in which the positioning pin is screwed.
In these conventional adjusting apparatuses, an operation of the positioning member for contacting members 611 and 712 is not defined. An operator practically activates an arm with a teaching device until the positioning pin contacts the members. Adjusting the origin requires accuracy, thus increasing a work load on the operator and increasing a working time. An erroneous handling by the operator during adjusting the origin may hurt the position pin and the arm. The operator attaches and detaches the positioning member. If the operator fails to attach the positioning member, the origin is not adjusted properly. If the operator fails to detach the positioning member after adjusting the origin and activates the robot, the positioning member and the arm of the robot arm may be damaged.